In the fall of 2013, a slow-moving rainstorm dumped more than 17 inches of water on Boulder in four days – about half the rain normally seen in a year. The volume of water overwhelmed the city’s infrastructure, leaving hundreds of ruined homes, scores of displaced families, and seven flood-related fatalities. The largest U.S. rescue airlift since Hurricane Katrina aided residents of mountain towns who had struggled in isolation, many of them without food or power, for a week or more.

In the weeks after the floodwaters receded, people returned to their homes, and life started getting back to normal. For Boulderites, that means returning to hiking, climbing, and mountain biking. But there was a problem: Most of Boulder’s cherished trails were closed; many of them had been destroyed.

Test of Principles

The headquarters for the International Mountain Bicycling Association (IMBA) is located in Boulder. For a quarter of a century, IMBA has championed the sport of mountain biking, attracting 90,000 individual supporters and more than 600 local mountain bike groups.

IMBA promotes the concept of “sustainable trail design” – the idea that where and how trails are built determine how well they will hold up to recreational use, and to weather. With the flood, Boulder’s vast trail network became a laboratory for testing IMBA’s trail design principles.

Illustration: Mark Schmidt

IMBA’S Guidelines for Building Sustainable Trails

IMBA has long emphasized the importance of sustainable trail design and construction. The fundamental principle is to build trails on the side of hills, not in flat areas or at the bottom valleys where water can accumulate.

A “contour trail” traverses the side slope of a hill – it’s characterized by a gentle grade, undulations called “grade reversals,” and a trail surface that tilts slightly toward the outer edge. These trail features help minimize erosion by allowing water to drain in a gentle, non-erosive manner called sheet flow. When water drains in thin, dispersed sheets, the trail can successfully resist erosion.

Water, the Destroyer

Steve and Morgan Lommele are Boulder residents with a better-than-average understanding of how a big rain event could cause an estimated $25 million in trail and habitat repairs. The Lommeles spent almost three years touring the United States in a specially equipped Subaru Outback, teaching mountain bike advocacy, trail-building best practices, and trail maintenance techniques as part of the Subaru/IMBA Trail Care Crew program.

“While on the road, we visited 43 states to teach local groups about the importance of building sustainable trails,” said Steve Lommele. “Minimal maintenance and minimal environmental impact are the defining traits of sustainably built trails. Whether we were building trails in the deserts of the Southwest or a Pacific Northwest rainforest, we always taught volunteers that water is the one thing that stands between a durable, enjoyable trail and an impossible-to-maintain scar on the land.”

Each weekend, the Lommeles worked with local mountain bikers, land managers, community leaders, and other trail users such as hikers and equestrians to share IMBA’s best practices for building sustainable trails and a thriving trail community. The Lommeles usually spent four whirlwind days in each location, sharing insights and best practices for trail building and community development.

The foundation of the Subaru/IMBA education program is the Trail Building School. In a three-hour presentation, participants learn to see trails in an entirely new way. What looks like a harmless path through the woods can, in fact, make or break an ecosystem. Most trail erosion is not caused by the way a trail is used – wheels, feet, paws, hooves – but rather how a trail is built.

Morgan and Steve’s 30 months on the road with the Subaru/IMBA Trail Care Crew ended in September 2012, when they returned to Boulder. But their contribution to the mountain bike community did not stop there.

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